This customer extrudes foamed PE sheet which is used to seal consumer products. Sheet thickness ranges from 4 to 40 mils and the material is used in applications such as food bottling or pill bottles. Wear is a critical factor as too much heat input due to screw wear causes poor control of foamed product sizing. In a foaming operation, process stability is very important. A reduction in output as a result of wear is not an issue compared to the poor quality product that results from an increase in melt temperature.
This is a 4-1/2”, 24:1 screw with a barrier flight and double mixers. The screw has a weld inlay of Colmonoy 56 on flight lands and hard chrome plating. At .010” of OD wear, process stability is affected and at .020” wear a screw is removed and rebuilt. The average screw life is about 12 to 14 months. The foamed PE also contains 4-5% titanium dioxide as a whitening agent.
Extreme Coatings encapsulated this screw with .010” of XC1000 with a mirror polish finish. The screw was installed in early May of 2006 and immediately melt temperature went down, and output up, as expected. The customer planned to remove and measure the screw at six months but high product demand did not allow the downtime.
At 12 months operation the process was as consistent as the day the screw was installed. Over these same 12 months, past Colmonoy 56 protected screws would have required many adjustments to compensate for wear. The screw was finally measured at 13 months of continuous operation and found to have .002” of total OD wear. This is nearly ten times longer wear life then the original feed screw protected with Colmonoy 56.
Wear in this process is limited to the flight land and mixer. This experience has helped develop our FliteGuard coating option. FliteGuard is an OD only coating which puts long wearing carbide at the point of wear, the flight land. Similar results can be achieved in most extrusion processes regardless of the polymer being processed. We do, however, limit this OD only option to processes in which no abrasive filler exists.
Approximate ten-fold improvement in screw wear life.
Extremely consistent process and output rate.